1. Field of the Invention
The present invention relates to a beamforming in a wireless communication system.
2. Description of the Related Art
A transmission end of a wireless communication system may generate and transmit an electric signal using an antenna, and a reception end of the wireless communication system may receive an electric signal transmitted by the transmission end via a radio channel. As a model for a gain of a received signal at the reception end that may be obtained via a beamforming gain at a transmission/reception antenna, a Friis equation may be used.
FIG. 1 illustrates a transmission end and a reception end of a wireless communication system according to the related art.
Referring to FIG. 1, a transmission end 110 and a reception end 120 of the related-art wireless communication system are shown. In a case where a transmission antenna having a beamforming gain Gt and a reception antenna having a beamforming gain Gr are separated by a distance d, the Friis equation is given by Equation 1.
                              P          r                =                              P            t                    ⁢                                                    G                t                            ⁢                              G                r                            ⁢                              λ                2                                                    16              ⁢                              π                2                            ⁢                              d                2                                                                        Equation        ⁢                                  ⁢        1            In Equation 1, Pr is power of a reception signal, Pt is power of a transmission signal, Gt is an antenna gain of a transmitter, Gr is an antenna gain of a receiver, λ is the length of a wavelength, and d is a distance between the transmitter and the receiver. The antenna gain of the transmitter may be referred to as a transmission beamforming gain, and the antenna gain of the receiver may be referred to as a reception beamforming gain.
Equation 1 may be applicable to free space. Therefore, when it is applied to a real system, some change may be given to Equation 1 according to characteristics of a radio channel. Equation 1 shows that power received in the receiver is proportional to a gain value of an antenna of the transmitter and the receiver. When transmission power and gain values of transmission beamforming and reception beamforming are raised via the Friss equation, a quality of a reception signal at the reception end may be improved.
FIG. 2 illustrates beam training in a wireless communication system according to the related art.
Referring to FIG. 2, a beamforming gain value at a Base Station (BS) 210 is expressed by GBS and a beamforming gain value at Mobile Station (MS) 220 is expressed by GMS. Herein, an MS may be referred as a User Equation (UE) and may be any portable electronic terminal that may access a wireless communication system. In order to increase efficiency of a transmission signal and a reception signal between the BS 210 and the MS 220, a process for matching a direction of a signal of the BS 210 having a specific direction with a direction of a signal of the MS 220 is needed. Generally, the process for matching the directions of signals is referred to as beam training. The beam training is a procedure for maximizing a power value of a reception signal in the Friss equation described with reference to FIG. 1 by accurately matching the direction of a transmission signal with the direction of a reception signal.
A beam training procedure at a downlink is described below with reference to FIG. 2. The BS 210 having a GBS, which is a fixed beamforming gain, transmits a unique sequence in a unique direction. The unique sequence is mapped to a beam index as 1:1, and the MS 220 may discriminate from which direction a best beam is received. The MS 220 may receive beams via a plurality of directions having a GMS, which is a fixed beamforming gain with respect to one beam index of the BS 210, and may then determine from which direction a signal having a highest power may be received. The above procedure may be applicable to an uplink in the same manner. In this case, the transmission end becomes the MS 220, and the reception end becomes the BS 210. For example, as illustrated in FIG. 2, in the case where the BS 210 has five beam indexes beam_1 211, beam_2 212, beam_3 213, beam_4 214, and beam_5 215, and the MS 220 has three beam indexes beam_1 221, beam_2 222, and beam_3 223, since the beam_3 213 of the BS 210 and the beam_2 222 of the MS 220 face each other, a combination of the beam_3 213 of the BS 210 and the beam_2 222 of the MS 220 may maximize reception power at the reception end.
Through the above beam training, an optimized beam index at the transmission end and an optimized beam index at the reception end may be determined so that reception power at the reception end may be maximized. The above beam training procedure may be performed periodically or may be event-driven. Generally, in the case where an MS has mobility, the beam training procedure is performed periodically, and in this case, when the beam training procedure is performed in a short period, a training overhead may be very large. Therefore, when maximization of power may be achieved more effectively during beam training, a training overhead by the beam training procedure may be reduced.
Therefore, a need exists for a system and method for controlling adaptive beamforming gain in a wireless communication system.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present invention.